1. Field of the Invention
This invention relates to a continuous method for producing polyorganosiloxanes by multiple-step hydrolysis and condensation of alkoxysilanes in the presence of hydrogen chloride and/or a compound that has at least one SiCl group and a solvent immiscible with water.
2. Description of the Background
The production of polyorganosiloxanes by hydrolysis of chlorosilanes or alkoxysilanes is known. Since the reaction rate of hydrolysis of chlorosilanes is greater than that of alkoxysilanes, the properties of the product can usually be controlled only with difficulty, and the reactions often end with the production of insoluble or useless end products.
To control the reactions, the chlorosilanes can be completely or partially alkoxylated and then hydrolyzed in a solvent immiscible with water. EP 691 362 describes a method in which alkoxysilanes with differing alkoxy groups are hydrolyzed.
The hydrolysis can be carried out continuously or discontinuously in homogeneous or heterogeneous phase, and using solvents miscible or immiscible with water. DD 228 550, for example, describes a continuous method for producing methyl resins starting with methylchlorosilanes. The drawback to this method consists of the fact that the hydrolysis products are of low molecular weight and have to be condensed in different ways, depending on their use.
Discontinuous methods have the advantage that during the hydrolysis and/or condensation reaction, the desired molecular weights or viscosities can be adjusted. However, the poor space-time yields are a drawback.
There is a need for an improved method for producing polyorganosiloxanes in a continuous and reproducible manner.